Move Magento2 top menu categories under second level

Topmenu.php

<?php
namespace Acme\Topmenu\Plugin\Theme\Block\Html;

use Magento\Framework\Data\Tree\NodeFactory;
use Magento\Framework\Data\TreeFactory;
use Magento\Framework\Data\Tree\Node;
use Magento\Framework\Data\Tree;

class Topmenu
{
    /**
     * @var NodeFactory
     */
    protected $nodeFactory;
  
    /**
     * @var TreeFactory
     */
    protected $treeFactory;
  
    /**
     * Topmenu constructor.
     * @param NodeFactory $nodeFactory
     * @param TreeFactory $treeFactory
     */
    public function __construct(
        NodeFactory $nodeFactory,
        TreeFactory $treeFactory
    ) {
        $this->nodeFactory = $nodeFactory;
        $this->treeFactory = $treeFactory;
    }
  
    public function beforeGetHtml(
        \Magento\Theme\Block\Html\Topmenu $subject,
        $outermostClass = '',
        $childrenWrapClass = '',
        $limit = 0
    ) {
        /** @var Node $menu */
        $menu = $subject->getMenu();
      
        /** @var Tree $menuTree */
        $menuTree = $menu->getTree();
      
        /*** move categories under second level ***/
        $categoriesNode = $this->getCategoriesNode($menuTree);
      
        $menuNodesCollection = $menu->getChildren();
      
        /** @var Node $categoryMenuItemNode */
        foreach ($menuNodesCollection as $categoryMenuItemNode) {
            $categoriesNode->addChild(clone $categoryMenuItemNode);
            $menuNodesCollection->delete($categoryMenuItemNode);
        }
        $menu->addChild($categoriesNode);
    }
  
    /**
     * @param Tree $tree
     * @return Node
     */
    private function getCategoriesNode(Tree $tree)
    {
        return $this->nodeFactory->create(
            [
                'data' => [
                    'name' => __('Category'),
                    'id' => 'categories',
                    'url' => '/categories/',
                    'has_active' => false,
                    'is_active' => false // (expression to determine if menu item is selected or not)
                ],
                'idField' => 'id',
                'tree' => $tree
            ]
        );
    }
}

app/code/Acme/Topmenu/etc/di.xml:

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Theme\Block\Html\Topmenu">
        <plugin name="acme_topmenu" type="Acme\Topmenu\Plugin\Theme\Block\Html\Topmenu" sortOrder="100"/>
    </type>
</config>

app/code/Acme/Topmenu/etc/module.xml:

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="Acme_Topmenu" setup_version="1.0.0">
        <sequence>
            <module name="Magento_Theme"/>
        </sequence>
    </module>
</config>

app/code/Acme/Topmenu/registration.php:

<?php
\Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::MODULE,
    'Acme_Topmenu',
    __DIR__
);